What could cause a disproportionate reduction in diastolic pressure?

I’m not asking for advice, just possible causes and mechanisms. I’m not looking to diagnose a health problem because I don’t think there is one; I’m trying to understand the intermediate cause-effects between exercise and blood pressure.

Let’s say you start with 120/80 80bpm blood stats. Then you exercise for a few months and it goes down to 110/65 65bpm; Diastolic pressure decreased proportionately more than systolic pressure. How come?